Someone driving in a car who's not paying attention for a moment and hits someone else feels like an accident to me. The same could have happened with a missile. Strictly speaking, everything has a cause. So by that definition there are no accidents.

That's all just arguing semantics though. I even agree with you that the term "accident" is not correct, despite what I wrote above. (Although I don't agree with your reasoning behind it). I'd prefer the term "incident".